Within photonic communication systems it is desirable to arrange individual circuits in a manner which allows the greatest flexibility of interconnection between them, so as to permit the overall system to be easily reconfigured. In addition, it is also desirable to arrange the individual photonic circuits so that the physical length of any interconnections is kept to a minimum, thereby decreasing inter-circuit transit time and optimizing the transmission rate within the overall communication system.
One such arrangement aimed at achieving these goals, which has gained acceptance in the industry, is edge-to-edge three-dimensional topology. In this topology, photonic circuit packs are arranged in stacked layers, each layer consisting of a parallel grouping of circuit packs. Typically, the circuit packs within a given layer are oriented orthogonally with respect to circuit packs of adjacent layers. Normally, interconnections between the layers are effected via optical fiber jumper cables which directly link a point on a circuit pack within one layer to a point on a circuit pack in another layer. This commonly results in large numbers of optical fiber jumpers running between any two layers within the orthogonal edge-to-edge three-dimensional topology. Jumper interconnection methods have proved expensive from both a material and labor cost stand point, and do not readily lend themselves to easing the complexity of system reconfiguration (large numbers of inter-layer jumpers can prove confusing and cumbersome to work with).
Alternate methodologies of interconnecting the circuit packs within an orthogonal edge-to-edge three-dimensional topology employ low-loss, short-length optical connectors (see "Orthogonal packaging for a photonic switching system", Y. Satoh, M. Kurisaka, T. Sawano, Optical Fiber Communication Conference 1992 Technical Digest Series, Vol. 5, p. 162, Feb. 1992). While these connectors minimize the length of the inter-layer optical fiber links, they introduce two inter-layer optical connections. Each fiber linked to a component on one layer is connected with one end of a short optical fiber, and the other end of that short optical fiber is connected to a fiber linked to a component in another layer. Naturally, optical losses and material costs increase with each additional inter-layer optical connection.
Furthermore, the short-length optical connectors do not offer much flexibility with respect to system reconfiguration. The optical connectors on one circuit pack of a particular layer each mate with particular optical connectors upon a second circuit pack of an adjacent layer. To reconfigure the system, the connections between the optical connectors and the individual components within each circuit pack would have to be physically rerouted. This would involve manually breaking existing optical connections between an optical connector and circuit pack components, and establishing a new connection to an alternate circuit pack component. Typically, such reconfiguring proves to be tedious, time consuming, and expensive.